This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to incorporation of a single-sided unipolar piezoelectric transducer driver for a disc drive.
Disc drives are used for data storage in modem electronic products ranging from digital cameras to computer systems and networks. Typically, a disc drive includes a mechanical portion, or head disc assembly (HDA), and electronics in the form of a printed circuit board assembly (PCB), mounted to an outer surface of the HDA. The PCB controls HDA functions and provides an interface between the disc drive and its host.
Typically, a HDA comprises a magnetic disc surface affixed to a spindle motor assembly for rotation at a constant speed and an actuator assembly position-controlled by a closed loop servo system. The actuator assembly supports a read/write head that traverses generally concentric magnetic tracks radially spaced across the disc surfaces. Disc drives using magneto resistive heads typically use an inductive element to write data to the tracks in the form of magnetic flux transitions and a magneto resistive element to read data, such as servo data, from the track during drive operations. Servo data are typically written to the track during the manufacturing process by a servo track writer and are used by the closed loop servo system for controlling read/write head position during drive operations.
Continued demand for disc drives with ever-increasing levels of data storage Continued demand for disc drives with ever-increasing levels of data storage capacity, faster data throughput and decreasing price per megabyte have led disc drive manufacturers to seek ways to increase the storage capacity and improve overall operating efficiencies of the disc drive. Present generation disc drives typically achieve areal densities of several gigabits per square centimeter, Gbits/cm2. Increasing recording densities can be achieved by increasing the number of bits stored along each track or bits per inch (BPI), generally requiring improvements in the read/write channel electronics, and/or by increasing the number of tracks per unit width or tracks per inch (TPI), generally requiring improvements in servo control systems.
One approach taken by disc drive manufacturers to improve servo control systems has been through the introduction of dual-stage actuator systems. One such system utilizes a suspension based bipolar piezoelectric transducer (PZT) operating in parallel with the VCM and driven by a bipolar driver. To date, attempts at utilizing more cost-effective single-sided unipolar drivers in a dual-stage actuator application have been unsuccessful since the D.C. component of the position signal and the D.C. component of the PZT driver affects both the VCM and the PZT transducer control signals.
As such, challenges remain and a need persists for advancing dual-stage actuator art with economical and effective solutions that overcome the constraints present in disc drives with dual-stage actuator systems.
The present invention provides an economical method for position-controlling a mechanical position of a micro-actuator of a disc drive, through use of a single-sided unipolar device driver. By supplying a bias voltage to the micro-actuator, rather than as an offset to a reference signal, to preset the mechanical position of the micro-actuator relative to a selected data track of the disc drive, the single-sided unipolar device driver can be used to adjust the position of the micro-actuator, in either a positive or negative position, relative to the preset position, through use of a single polarity input voltage.
In a preferred embodiment the micro-actuator is a bipolar piezoelectric transducer that responds to positive voltage input by expanding in a predetermined direction, while contracting in response to the application of a negative voltage. The bias voltage supplied to the piezoelectric transducer is a positive voltage that expands the piezoelectric transducer by substantially one half of the expansion capabilities of the piezoelectric transducer. Correction signals generated by the control circuit of the disc drive are effective in changing the mechanical position of the micro-actuator relative to a selected data track when the correction signal has a voltage in the range of between a positive xe2x80x9c+xe2x80x9d or a negative xe2x80x9cxe2x88x92xe2x80x9d voltage substantially equal to the applied bias voltage. Correction signals of negative voltage reduce the voltage supplied to the micro-actuator, thereby causing the piezo electric transducer to contract. Whereas correction signals of positive voltage increase the voltage supplied to the micro-actuator, thereby causing the piezoelectric transducer to expand.
By confining the correction signals to a voltage range between a positive xe2x80x9c+xe2x80x9d or negative xe2x80x9cxe2x88x92xe2x80x9d voltage substantially equal to the applied bias voltage, a single-sided unipolar driver is effective in controlling the bipolar piezoelectric transducer. And, as the piezoelectric transducer is affixed to the load arm of the head stack assembly, changes in mechanical position of the micro-actuator relative to the selected data track results in changes in mechanical position of the read/write head relative to the selected data track, thereby facilitating position-control of the read/write head relative to the selected data track.
These and various other features and advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.